In a small bowl, combine the espresso and Kahlua. Set aside to cool completely. If the espresso mixture is hot the ladyfingers will absorb too much liquid and fall apart easily. Using a whisk, beat the egg yolks and 2 tablespoons of sugar in a medium metal bowl set over a saucepan of simmering water until the mixture is pale and thick and forms a ribbon when the whisk is lifted.

Cool for 5 minutes. Place the mascarpone in a large bowl. Stir half of the yolk mixture into the mascarpone to lighten, then fold in the remaining yolk mixture. In another large bowl beat the whipping cream and the remaining 2 tablespoons of sugar with the electric mixer just until stiff peaks form.

Fold the whipping cream into the mascarpone mixture and set aside.

Quickly dip enough of the cookies into the Kahlua mixture to cover the bottom of a 9 x 13 glass dish or pan. Cover with half of the marscapone mixture Top with another layer of dipped cookies and the remaining marscapone mixture.

Sift the cocoa powder over the tiramisu. Refrigerate until set, at least 2 hours (overnight is best.)